The cracks which appear in building works embedded in concrete have several causes: microcracking provoked or due to porous concrete, shrinkage cracks, cracks due to loads settling, to resumption of concreting, to construction joints, etc. Depending on the geographical location of the building work in question, these cracks are filled to a greater or lesser extent with water, and in general they remain constantly in a damp state.
In order to be effective, the sealing of building works must remove the water from the crack prior to stopping the crack. In conventional manner, use is made of the injection technique together with acrylic type resins which polymerize without difficulty in the presence of water. For example, the "Bulletin Technique de la Suisse Romande" of 27 July 1963 describes a mixture for sealing by injection, the mixture comprising an aqueous solution of acrylamide and of methylene bisacrylamide together with a redox catalyst. The mixture has the advantage of being easily injectable since its viscosity is close to that of water until it sets, and of being usable even under the dampest of conditions. In addition, its limiting strength is reached very quickly after it begins to set. However, in spite of these undoubted advantages, this mixture based on acrylamide is not widely used, apparently because of certain difficulties in implementing it.
On worksites, the two components, namely the acrylamide solution and the redox catalyst, are mixed by hand immediately before injection by non-specialized personnel without any verification means. Any mistake in the mixture proportions or any degradation of the catalyst can give rise to major consequences, particularly with respect to setting time which is initially selected as a function of the sealing problem to be solved. In addition, if the mixture contains excess redox catalyst, then the excess catalyst diffuses into the aqueous medium of the building work, and if that medium is reinforced concrete, then the steel structure therein is damaged.
A solution has already been proposed to this difficulty in implementation by providing a machine as described in French Pat. No. FR-A 83 16 253 in which the two components are fed, mixed, and injected automatically in an adjustable manner.
However, the difficulty is not completely overcome in the event of the machine malfunctioning or in the event of the operator setting it wrongly. There is no way of detecting such malfunctioning or wrong setting immediately.